The alpha subunit of the human granulocyte-macrophage colony-stimulating factor receptor signals for glucose transport via a phosphorylation-independent pathway.

Abstract

The receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) is composed of an a and B3 subunit, which together form the high-affinity receptor. The a subunit by itself binds ligand at low affinity, whereas the isolated (8 subunit does not bind GM-CSF. It is generally believed that the high-affinity receptor is responsible for the multiple functions of GM-CSF and that the isolated a subunit (GMRa) does not transduce a signal. Xenopus laevis oocytes injected with RNA encoding human GMRa expressed up to 1010 low-affinity sites for GM-CSF (Kd = 6 nM). GM-CSF binding to the a subunit expressed in Xenopus oocytes caused activation of 2-deoxyglucose transport through endogenous glucose transporters. 2-Deoxyglucose transport was stimulated by similar low concentrations of GM-CSF in HL-60 leukemia cells as well as normal human neutrophils and Xenopus oocytes expressing GMRa. Engagement of the isolated a subunit in oocytes did not lead to protein phosphorylation or tyrosine phosphorylation of mitogen-activated protein kinase (MAP kinase). Staurosporin and genistein inhibited GM-CSFinduced tyrosine phosphorylation of MAP kinase in human neutrophils and HL-60 cells without affecting GM-CSFstimulated uptake of 2-deoxyglucose. These results provide direct evidence that the isolated a subunit signals for hexose transport and can do so without engagement of the kinase cascade. Our data also indicate that signaling for hexose uptake may occur in a phosphorylation-independent manner in cells expressing the high-affinity GM-CSF receptor.The receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) is composed of an a and ( subunit, and the a subunit (GMRa) by itselfbinds ligand at low affinity (Kd = 3-7 nM) (1-6). The isolated 8 subunit (GMR(3) does not bind GM-CSF; however, it associates with GMRa to form a high-affinity receptor (Kd = 20-40 pM) (3-6). GM-CSF receptors are present on myeloid progenitors and mature neutrophils, eosinophils, and mononuclear phagocytes (7)(8)(9)(10)(11)(12)(13). GMRa is also present in some nonhematopoietic cells, such as placenta and melanoma cells (1,14,15), while the GMR(8 is mainly restricted to hematopoietic cells (3-5, 12).It is generally believed that the biological functions exerted by GM-CSF are mediated by the high-affinity receptor and that the isolated GMRa does not transduce a signal (3-6, 16, 17). GMRa, however, binds GM-CSF and in association with GMR,8 transduces signals involving protein phosphorylation (2,(18)(19)(20). To examine the functional capability of the isolated a subunit, we expressed it in Xenopus laevis oocytes and discovered that it could signal for glucose transport without involving the phosphorylation of mitogen-activated protein kinase (MAP kinase). MATERIALS AND METHODSComplementary DNAs for the human GMRa (21) and the human glucose transporter 4 (GLUT4) (22) cloned in pBluescript (Stratagene) were linearized by digestion with restriction enzymes, and the sense or antisense RNA was transcribed in vitro (23). Stage V and VI oocy...

Effect of granulocyte-macrophage colony-stimulating factor deficiency on ovarian follicular cell function

“…The present study demonstrated that COCs only express the α-subunit of the GM-CSFR. Thus, COCs are unlikely to respond to GM-CSF, although there are some reports that the free α-subunit can facilitate glucose uptake and thereby promote viability and proliferation in certain cell lineages (Ding et al, 1994). In contrast, MGCs were found to express both the α-and the β-subunits.…”

“…In the absence of β-subunit, GM-CSF binds GM-CSFRα with low affinity and, in some cells, this may lead to improved glucose transport (Ding et al, 1994). However, high affinity ligand binding is conferred by the β-subunit, which results in rapid intracellular tyrosine phosphorylation required to elicit the full range of GM-CSFdependent effects on cell proliferation and differentiation (Duronio et al, 1992).…”

Acute regulation of glucose transport in a monocyte–macrophage cell line: Glut-3 affinity for glucose is enhanced during the respiratory burst

“…Alternatively the GM-CSF α-chain might have signalling functions of its own. In this context it is interesting to note that the GM-CSF α-chain seems to be able to regulate glucose transport in Xenopus oocytes and in certain melanoma cell lines independently of βc [37,38].…”

Molecular imaging of lung glucose uptake after endotoxin in mice

“…Inflammatory activators such as PMA, the tripeptide formyl-methionyl-leucyl-phenylalanine, and granulocyte/monocyte colony-stimulating growth factor each increase glucose uptake by neutrophils (13,43). Because inflammatory cytokines are known to be potent neutrophil activators in general, and since priming with TNF-␣ (25, 26) has been specifically implicated as a major factor affecting neutrophil glucose uptake, we first tested the effect of inhibiting the effects of TNF-␣ (either with a specific monoclonal antibody or in mice defective for the TNF-␣ receptors) on lung [ 18 F]FDG uptake after Etx.…”